It is known to provide thermal compresses in the form, for example, of a plastic envelope containing a chemical which absorbs heat on the addition of water thereto and in which the water is retained in a separate envelope which is susceptible of being ruptured so that the necessary thermal change or thermal reaction will take place when the water is permitted to come together with the aforementioned chemical. Such an article of manufacture is described, for example, in U.S. Pat. No. 2,907,173 which issued to A. Robbins on Oct. 6, 1959. In this patent is described a refrigerating package which includes an outer sealed envelope coated with a metallic foil and containing a dry freezing chemical mixture with a sealed envelope contained within the outer sealed envelope and containing a hydrous substance, the inner envelope being susceptible of being ruptured without breaking the outer envelope. This patent discloses, among other chemicals, the use of ammonium nitrate, sodium carbonate and the like which upon being exposed to water or to a hydrous chemical form a cooling mixture. The envelopes in which the chemicals are retained and in which the water or hydrous chemical are retained are fabricated, for example, of polyethylene, vinyl or acetate. The inner bag is sufficiently thin that when the compress is twisted or compressed, the inner envelope is torn permitting the material therein to escape and intermingle or mix with the other chemical contained in the outer envelope.
A further description of a thermal compress in the form of a refrigerating package is given in U.S. Pat. No. 2,925,719 which issued on Feb. 23, 1960 to A. Robbins et al. This patent describes a refrigerating package comprising a sealed outer envelope formed of flexible fluid-tight transparent sheet plastic material, a refrigerating chemical disposed within this outer envelope, a water soluble coloring dye disposed in the outer envelope and a sealed water containing inner envelope formed of a flexible fluid-tight transparent sheet plastic material disposed within the outer envelope. The inner envelope is of smaller dimensions and has a lower bursting strength than the outer envelope. The interior of the outer envelope is partially evacuated of air and the water within the inner envelope is normally isolated from the refrigerating chemical. The exterior surfaces of the walls of the inner envelope are directly engageable by the interior surfaces of the walls of the outer envelope whereby an inwardly directing force applied against the outer envelope imposes a direct mechanical force on the inner envelope to rupture the latter without breaking the outer envelope. Thereby there is effected the mixing of the water with the refrigerating chemical and with a coloring dye.
Among the problems of the packages provided by A. Robbins in the aforesaid patents is the problem that sometimes considerable force is required to burst the inner envelope in order to provide for a mixing of the thermally reactive chemicals. In addition it is sometimes found that a certain technique is required to burst the inner envelopes and that this technique is not always easily effected. In addition there are problems of premature liquid leakage and furthermore it is not possible to construct packages of predictable operation since it is not possible to predict where the inner envelopes will burst and the degree to which there will exist a passageway between the substance contained in the inner envelopes and the substance surrounding the same.
Some of the above problems are to a slight extent solved by Caillouette et al in U.S. Pat. No. 3,175,558 which issued on Mar. 30, 1965. Herein is described a therapeutic pack for the thermal treatment of a person which pack includes a container bag of flexible proof material, chemical substances within the container bag including a liquid component and a separate non-liquid component for producing a temperature changing reaction upon the mixture of these components within the bag, there being provided a fracturable section for containing the liquid component apart from the other component so that the components can be controllably mixed to give the desired thermal result. In this patent is furthermore described the coating of at least a portion of one of the chemical components with a soluble coating in order that the mixing of the substances be spread out over a greater period of time. In addition, there is described an absorbent pad corresponding in size to the container bag and a wrapper of flexible material for holding the pad and the container bag together whereby the pad can be held adjacent to the person being treated.
The difficulty with one embodiment of the invention disclosed by Caillouette et al is that the solid chemical substance is generally retained all in one portion of the resulting enclosure after the chemicals are permitted to mix, while at the same time, the package provided is of extended length and difficult to pack and ship as well as to manufacture with a high degree of consistency as regards the subsequent usage thereof. This embodiment employs opening tabs but employs them in a construction wherein the fluid forces which are exerted on the closure between the substances can be expected to lead to fluid leakage and consequently premature operation of the package. The other embodiment disclosed by Caillouette et al. is subject to the same deficiencies as have been noted hereinabove with respect to the Robbins Patents.